Process for the utilization of refinery C4 streams

ABSTRACT

A process is disclosed for preparing a C 4  stream for feeding to an alkylation process which reacts isobutane with butene to produce isooctane. The C 4  stream is treated in a first distillation column reactor to remove dienes and mercaptans and separate out any C 5 &#39;s which might be present. The treated C 4 &#39;s are then fed to a second distillation column reactor that concurrently isomerizes 1-butene to 2-butene and splits the normal C 4 &#39;s from the iso C 4 &#39;S. The iso C 4 &#39;s are then fed to a third distillation column reactor where a portion of the isobutene is saturated to isobutane. The C 4 &#39;s from the isomerization/splitter are combined with the C 4 &#39;s from the hydrogenation unit and fed to a cold acid alkylation unit. The third distillation column may also oligomerize a portion of the isobutene to diisobutene in the upper end which is saturated in the bottom of the column to isooctane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the utilization of refinery C₄ streams containing iso and normal butanes and butenes. More particularly the invention relates to a process for producing alkylate feed from a mixed C₄ stream. In one embodiment the invention relates to a process which produces isooctane in addition to alkylate feed.

2. Related Information

Refinery C₄ streams have recently been utilized in the production of methyl tertiary butyl ether (MTBE) for use as an oxygenate additive and octane improver in motor gasolines. Processes and catalyst systems for their use in this manner have been developed over the years and include U.S. Pat. Nos. 4,215,011; 4,242,530; 4,232,177; 4,307,254; 4,336,407; 4,375,576 and like patents.

Refinery C₄ streams have also been used as the source of butenes and isobutane for feed to cold acid alkylation processes which produce isooctane. Generally there has been an imbalance in the amount of isobutene and butenes in refinery C₄ streams which have led to the use of the MTBE processes which utilize the isobutene, effectively removing it from the C₄ stream.

Environmental concerns have led at least the state of California to ban the use of MTBE in gasoline. Other processes for the balancing of the iso/normal butenes are now required.

SUMMARY OF THE INVENTION

Briefly, the present invention is an integrated process for the preparation of paraffin alkylate in which a C₄ hydrocarbon feed is first treated to remove dienes and mercaptans, for example, by reacting the dienes and mercaptans to form sulfides, separating the C₄'s from heavy material comprising the sulfides, for example, by fractionation. The treated C₄ feed is then subjected to isomerization to convert butene-1 to butene-2 and the iso C₄'s are separated from the normal C₄, for example by fractionation. The iso C₄ portion is hydrogenated to convert isobutene to isobutane and the C₄ fractions reunited and subjected to paraffin alkylation to produce an alkylate comprising isooctane.

In a preferred embodiment the C₄ stream is first treated in a first distillation column reactor to remove dienes and mercaptans and separate out any C₅'s which might be present. The treated C₄'s are then fed to a second distillation column reactor that concurrently isomerizes 1-butene to 2-butene and splits the normal C₄'S from the iso C₄'S. The iso C₄'s are then fed to a third distillation column reactor where a portion of the isobutene is saturated to isobutane. The C₄'s from the isomerization/splitter are combined with the C₄'S from the hydrogenation unit and fed to a cold acid alkylation unit.

In one embodiment the third distillation column reactor also oligomerizes a portion of the isobutene to diisobutene in the upper end which is saturated in the bottom of the column to isooctane. A portion of the unreacted isobutene is also hydrogenated to isobutane. The remainder of the iso C₄'s are fed to alkylation unit.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow diagram in schematic form of one embodiment of the invention.

FIG. 2 is a flow diagram in schematic form of a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 a flow diagram of one embodiment of the invention is shown. Feed to a cold acid alkylation unit must be low in dienes and mercaptans. To this end the mixed C₄ feed in flow line 101 is treated in a distillation column reactor 10 containing a bed 12 thioetherification catalyst which reacts the mercaptans with dienes in the feed to produce higher boiling sulfides which are removed in the bottoms in flow line 103 along with any C₅'S in the feed. Alternatively this column may be operated to send the C₅'s overhead with the C₄'s and to recover the C₅'S in the bottoms from column 20 along with the nC₄'s in line 105. Catalysts which are useful for this reaction include the Group VIII metals, such as palladium and nickel. Generally the metals are deposited as oxides on an alumina support. The supports are usually small diameter extrudates or spheres. A suitable catalyst for the reaction is 58 wt. % Ni on 8 to 14 mesh alumina spheres, supplied by Calcicat, designated as E-475-SR. Typical physical and chemical properties of the catalyst as provided by the manufacturer are as follows:

TABLE I Designation E-475-SR Form Spheres Nominal size 8 × 14 Mesh Ni wt. % 54 Support Alumina

The hydrogen rate to the reactor, which is fed along with the mixed C₄ feed in flow line 101, must be sufficient to maintain the reaction which is understood to be the “effectuating amount of hydrogen” as that term is used herein, but kept below that which would cause flooding of the. Generally, the mole ratio of hydrogen to diolefins and acetylenes in the feed is at least 1.0 to 1.0, preferably at least 2.0 to 1.0 and more preferably at least 10 to 1.0.

The catalyst also catalyzes the selective hydrogenation of the polyolefins contained within the feed and to a lesser degree the isomerization of some of the mono-olefins. Generally the relative absorption preference is as follows:

-   -   (1) sulfur compounds     -   (2) diolefins     -   (3) mono-olefins

If the catalyst sites are occupied by a more strongly absorbed species, reaction of these weaker absorbed species cannot occur.

The reaction of interest is the reaction of the mercaptans and/or hydrogen sulfide (H₂S) with diolefins. In the presence of the catalyst the mercaptans will also react with mono-olefins. However, there is an excess of diolefins to mercaptans and/or hydrogen sulfide (H₂S) in the feed and the mercaptans preferentially react with them before reacting with the mono-olefins. The equation of interest which describes the reaction is:

Where R, R₁ and R₂ are independently selected from hydrogen and hydrocarbyl groups of 1 to 20 carbon atoms. If there is concurrent hydrogenation of the dienes, then hydrogen will be consumed in that reaction. The only mercaptans expected to be present in the mixed C₄ feed are the lower boiling ones such as methyl mercaptan.

The treated feed is taken overheads via flow line 102 and then fed to a second distillation column reactor 20 which contains a bed 22 of isomerization catalysts. In the second distillation column reactor 20 the isobutene, isobutane and unreacted 1-butene are concurrently separated from normal butanes and both isomers of 2-butene. Concurrently 1-butene is isomerized to 2-butene to help in the separation. Essentially cis and trans 2-butene and normal butane are removed as bottoms via flow line 105 while the remaining C₄'s (isobutane and isobutene) are removed as overheads via flow line 104. The 2-butenes are preferred over 1-butenes for alkylation, since the 2-butene alkylate product has a higher octane number.

The distillation column reactor is generally operated at overhead temperatures in the range of 80 to 180° F., more preferably 100 to 150° F. at pressures in the range of 50 to 110 psig (bearing in mind the effect of pressure on temperature as discussed above). In its more preferred embodiments the present process is operated under conditions, particularly temperature and pressure, which tend to exclude butene-2 from contact with the catalyst while holding the butene-1 in contact with the catalyst. Thus, as butene-1 is isomerized to butene-2 it drops down in the column away from the catalyst and is removed as bottoms.

A reflux is preferably included in the system. The reflux ratio could vary over the rate 0.5:1 to 33:1. In practice, the higher ratio may be used to compensate for a short catalyst bed such as required for experimental work. In commercial size units the catalyst bed would be provided so that lower reflux and hence higher unit productivity could be obtained at lower operating cost. In a modification designed to optimize the operation of the embodiments of both FIG. 1 and FIG. 2 the catalyst bed 22 may be divided into several smaller zones with conventional distillation staging between each zone (not shown).

A catalyst suitable for the present process is 0.5% PdO on ⅛″ Al₂O₃ (alumina) extrudates, hydroisomerization catalyst, supplied by Engelhard Industries. The catalyst is believed to be the hydride of palladium which is produced during operation. The hydrogen rate to the distillation column reactor must be sufficient to maintain the catalyst in the active form because hydrogen is lost from the catalyst by hydrogenation. The hydrogen rate must be adjusted such that there is sufficient hydrogen to replace hydrogen lost from the catalyst which is understood to be the “effectuating amount of hydrogen” as that term is used herein but kept below that required for hydrogenation of butenes or to cause flooding of the column. Generally, the mole ratio of hydrogen to C₄ hydrocarbon fed to the bed of the present invention will be about 0.01 to 0.60, preferably 0.01 to 0.10.

Another suitable catalyst for the reaction is 0.34 wt % Pd on 7 to 14 mesh Al₂O₃ (alumina) spheres, supplied by United Catalysts Inc. designated as G-68C. Typical physical and chemical properties of the catalyst as provided by the manufacturer are as follows:

TABLE II Designation G-68C Form Sphere Nominal size 7 × 14 mesh Pd. wt % 0.3 (0.27-0.33) Support High purity alumina

Finally the separated isobutene (along with trace amounts of 1-butene and isobutane) are fed via line 104 to a third distillation column reactor 30 above a bed 32 of hydrogenation catalyst where a portion of the isobutene is saturated to isobutane. Hydrogen for the reaction is fed below the bed via flow line 106. The Pd and Ni catalysts are useful for this hydrogenation also. A distillation is carried out to have a condensing liquid in the column which the hydrogen is occluded which improves the contact between the hydrogen, catalyst and hydrocarbon. Thus an overhead is taken via flow line 107 with the condensible material being condensed in condenser 34 and returned to the distillation column reactor 30 as reflux via flow line 108. Vapors are removed via flow line 110

The bottoms from this distillation column reactor in flow line 109 along with the bottoms from the separation/isomerization column in flow line 105 are fed to a cold acid alkylation process.

Referring now to FIG. 2 a second embodiment of the invention is shown with the same reference numerals depicting the same items as in FIG. 1. The first two distillation column reactors 10 and 20 are identical to that of FIG. 1. The third distillation column reactor 30, however has a bed of acidic cation exchange resin in an upper bed 33 which oligomerizes a portion of the isobutenes to diisobutene which is then hydrogenated in a lower bed of hydrogenation catalyst 32 along with a portion of the isobutene. The hydrogenated diisobutene is 2,2,4-trimethyl pentane or isooctane of 100 octane number and is taken as bottoms via flow line 109. The overheads product containing the iC₄'s and iC₄='s are taken via flow line 111 and fed to the cold acid alkylation unit (not shown) along with the bottoms from the second distillation column reactor 20.

Preferably the hydrogenation in column 30 is carried out as described in copending U.S. patent application Ser. No. 09/474,192 filed Dec. 29, 1999, which is incorporated herein in its entirety, by concurrently passing the feed containing diisobutene and hydrogen downflow through a reaction zone containing a hydrogenation catalyst at a pressure of less than 300 psig pressure, preferably less than 275 psig, for example less than 200 psig, and for example at least about 100 psig at a temperature within the range of 300° F. to 700° F. to produce an effluent, said temperature and pressure being adjusted such that the temperature of the effluent is above its boiling point and below its dew point, whereby at least a portion but less than all of the material in said reaction zone is in the vapor phase. Preferably the weight hourly space velocity (WHSV), i.e., the weight of petroleum feed per hour per volume of catalyst is greater than 6 hr⁻¹, preferably greater than 8 hr⁻¹ and more preferably greater than 15 hr^(—1).

The preferred alkylation process comprises alkylation of isoparaffin with olefin comprising contacting a fluid system comprising acid catalyst, isoparaffin and olefin in concurrent flow, preferably downflow into contact in a reaction zone with internal packing, such as, a coalescer under conditions of temperature and pressure to react said isoparaffin and said olefin to produce an alkylate product. Preferably, the fluid system comprises a liquid and is maintained at about its boiling point in the reaction zone.

The reaction may be carried out in an apparatus comprising a vertical reactor containing a coalescer in the reaction zone, which may comprise the entire column or a portion thereof.

The process is more completely described in co-owned patent application having docket number CDT 1769/79 (U.S. Ser. No. 60/323,227 filed Sep. 14, 1901) which is hereby incorporated by reference.

The preferred alkylation process employs a downflow reactor packed with contacting internals or packing material (which may be inert or catalytic) through which passes a concurrent multi phase mixture of sulfuric acid, hydrocarbon solvent and reactants at the boiling point of the system. Adjusting the pressure and hydrocarbon composition controls the boiling point temperature. The reactor is preferentially operated vapor continuous but may also be operated liquid continuous. The pressure is preferentially higher at the top of the reactor than at the bottom. Adjusting the flow rates and the degree of vaporization controls the pressure drop across the reactor. Multiple injection of olefin is preferred. The product mixture before fractionation is the preferred circulating solvent. The acid emulsion separates rapidly from the hydrocarbon liquid and is normally recycled with only a few minutes residence time in the bottom phase separator. Because the products are in essence extracted from the acid emulsion, the reaction and/or emulsion promoters may be added without the usual concern for breaking the emulsion. The process may be described as being hydrocarbon continuous as opposed to acid continuous.

The coalescer comprises a conventional liquid-liquid coalescer of a type which is operative for coalescing vaporized liquids. These are commonly known as “mist eliminators” or “demisters”. A suitable coalescer comprises a mesh such as a co-knit wire and fiberglass mesh. For example, it has been found that a 90 needle tubular co-knit mesh of wire and fiberglass such as manufactured by ACS Industries LLC of Houston, Tex., can be effectively utilized, however, it will be understood that various other materials such as co-knit wire and Teflon (Dupont™), steel wool, polypropylene, PVDF, polyester or various other co-knit materials can also be effectively utilized in the apparatus. 

1. An integrated process for the preparation of paraffin alkylate from a C4 feed containing isobutane, isobutene, normal butane, butene-1, butene 2, dienes and mercaptans comprising: removing dienes and mercaptans from said C₄ feed; isomerizing a portion of the butene-1 to butene-2; separating iso C₄ components from the normal C₄ components; hydrogenating a portion of the isobutene in said iso C₄ components to isobutane; recombining said normal C₄ components and said iso C₄ components and alkylating isobutane and normal butenes in said recombined C₄ components to produce an alkylate comprising isooctane.
 2. The process according to claim 1 wherein said removing of dienes and mercaptans comprises reacting said dienes and mercaptans in the presence of a thioetherification catalyst and hydrogen under thioetherification conditions to form sulfides and fractionating the resultant mixture to separate a heavy portion comprising said sulfides.
 3. The process according to claim 1 wherein said isomerizing is carried out in the presence of an isomerization catalyst and hydrogen under isomerization conditions.
 4. The process according to claim 1 wherein said separating is by fractionation.
 5. The process according to claim 1 wherein said alkylating is carried out in the presence of an acid catalyst under alkylation conditions.
 6. An integrated process for the preparation of paraffin alkylate from a C₄ feed containing isobutane, isobutene, normal butane, butene-1, butene 2, dienes and mercaptans comprising: reacting said dienes and mercaptans in the presence of a thioetherification catalyst and hydrogen under thioetherification conditions to form sulfides and fractionating the resultant mixture to separate a heavy portion comprising said sulfides; isomerizing a portion of the butene-1 to butene-2 in the presence of an isomerization catalyst and hydrogen under isomerization conditions; separating iso C₄ components from the normal C₄ components by fractionation; hydrogenating a portion of the isobutene in said iso C₄ components to isobutane; recombining said normal C₄ components and said iso C₄ components and alkylating isobutane and normal butenes in said recombined C₄ components in the presence of an acid catalyst under alkylation conditions to produce an alkylate comprising isooctane. 